1. Field of the Invention
An apparatus and a method consistent with the present invention relate to a filter and a method for fabricating the same and, more particularly, to an integrated filter including a film bulk acoustic resonator (FBAR) and a surface acoustic wave (SAW) resonator and a method of fabricating the same.
2. Description of the Related Art
With the rapid popularization of mobile communication devices representative of portable phones, demand for compact, light filters and duplexers used in the mobile communication devices has increased. FBARs and SAW resonators are used as members for realizing filters.
The FBARs can be mass-produced in a small size and at a minimum cost. The FBARs can also realize quality factor (Q) values that are desirable characteristics of filters.
In general, such an FBAR includes a resonance part in which a lower electrode, a piezoelectric layer, and an upper electrode are sequentially stacked on a substrate. Describing the operation principle of the FBAR, an electric energy is applied to the lower and upper electrodes to induce an electric field varying with time in the piezoelectric layer, and the electric field generates a bulk acoustic wave in a direction toward which the resonance part vibrates, in the piezoelectric layer so as to produce a resonance.
SAW filters have simple structures and thus can be mass-produced. In other words, the SAW filters include inter-digital transducer (IDT) electrodes fabricated in comb structures on piezoelectric substrates. Since patterns of the comb structures of the IDT electrodes are minute in this case, it is difficult to design the SAW filters so as to be used in a frequency band having a predetermined intensity or more. Thus, the SAW filters are generally used in a low frequency band.
In the prior art, a filter is realized using a hybrid method of connecting an FBAR and a SAW resonator to be used in various frequency bands. In this case, a usable frequency band is widened. However, a connection process is complicated, and thus yield is reduced.
Also, a plurality of resonators separately fabricated are connected to one another and used. Thus, the entire size of the filter increased. As a result, it is difficult to use the filter in a compact electronic device such as a portable phone.